She was speaking after being elected to the Stray, Woodlands and Hookstone division as one of 10 Liberal Democrat councillors which will represent the Harrogate district on the new North Yorkshire Council.
The Conservatives won nine seats on the new unitary authority, while one Green Party candidate and one Independent were also elected.
Councillor Marsh said: "I'm so thrilled that people have got behind the strong Liberal Democrat message which we have been trying to get out for many years.
"These people have suddenly heard our voices again and it is amazing.
"At last there is going to be more Liberal Democrat voices instead of what has previously just been Conservatives, Conservatives, Conservatives.
"It is about time other voices were heard."
Although the Liberal Democrats have won the most seats in the Harrogate district, the Conservatives still maintain majority control across North Yorkshire after securing 47 of the total 90 seats on the new council which will launch in April 2023.
The new unitary authority will replace the existing county, district and borough councils, including Harrogate Borough Council which has been under Conservative control since 2010.
The Lib Dems previously ran the council for eight years between 1994 and 2002 when councillor Marsh served as mayor during a one-year term.
She added: "The Conservatives should realise that being elected isn't just about having the title of councillor.
"You have got to be on the council for a reason - and that is to improve the area you represent."
By Jacob Webster, Local Democracy Reporter